The surface of a submerged membrane module needs to be continuously decontaminated via aeration to prevent the contaminants adhered to the surface of the membrane in microbial reactor tank or a raw water tank from causing decrease in the filtration performance. For this purpose, an air diffuser including an air diffusion pipe is disposed under a membrane cassette to inject air, thereby cleaning the membrane. Generally, the air diffusion pipe has a circular tubular shape and includes a plurality of air diffusion holes formed at regular intervals to evenly distribute air throughout the membrane.
In order to improve cleaning efficiency, an attempt has been made to use an aerator which holds a certain amount of air discharged from an air diffusion pipe and discharges large bubbles at the same time (see FIG. 1). However, the aerator has a problem in that a vortex of air is generated at each corner of an airflow path (a first cavity, a first chamber, and a second chamber). Such a vortex of air interferes with air flow, such that the air cannot be discharged from the aerator at the same time. As a result, an initial discharge speed of air from the aerator is reduced, and large bubbles cannot be continuously discharged.
Therefore, there is a need for an aerator which can overcome such a problem, thereby providing improved cleaning efficiency.
The background technique of the present invention is disclosed in U.S. Pat. No. 8,038,882.